A well-motivated and common working hypothesis is that learning involves some change in the functional connectivity among nerve cells, probably at their synaptic interconnections. In searching for a likely synaptic candidate for such changes in the mammalian nervous system, the phenomenon of the long-term synaptic potentiation (LTP) is an obvious choice, for three reasons: LTP can be induced by very brief tetanic stimulation, it lasts hours, days, or weeks; and the conditions required for its induction bear a tantalizing similarity to some of the laws of classical conditioning. The present proposal has three interrelated objectives. The first goal is to determine and quantify the spatial and temporal rules governing the induction, magnitude and duration of associative LTP. The second goal is to provide evidence on the basis of the enhanced synaptic efficacy. The third goal is to determine the mechanism responsible for the associativity. The fact that associative LTP occurs in the in vitro hippocampus is extremely important because this is the only known vertebrate preparation in which a promising synaptic model for associative memory has been demonstrated and which is amenable to many of our most powerful analytical neurophysiological techniques.